An antenna is usually connected to a transmitter or receiver by way of a feed line. Antennas for use at radio frequencies are effective over a limited frequency range. When operation is required over a wide frequency range it is common to use multiple antennas with each antenna optimized for a specific narrow band of frequencies. The desired antenna is manually selected by a switch or other means that connects that antenna's feed line to the transmitter or receiver.
If the antenna is a so-called active antenna (i.e., includes an antenna (pre-) amplifier), the antenna amplifier can easily be supplied with power and switched on and off on an individual basis in order to save power when the antenna is not used. Furthermore, an antenna diagnosis can be simply performed for each individual antenna. However, in such an antenna system for each antenna an individual feed line must be provided making such a system costly, space consuming and heavy, thus, less suitable for automotive applications.
Also common are systems in which multiple (active) antennas are connected to multiple receivers and/or transmitters via a single feed line. When using a single feed line, however, antenna selection, power supply, on/off switching of active antennas and antenna diagnosis are difficult to realize, provided they can be realized at all. Thus, there is a need to provide a multi-band, multi-antenna system that overcomes the above-mentioned drawbacks.